The present invention relates to the photometric analysis of blood properties to monitor changes in blood volume, blood proteins concentration, cardiac output and other hemodynamic parameters. More particularly, the invention includes a method and apparatus for employing a single light emitter and a single photodetector, the single photodetector is oriented with respect to the emitter to minimize a scattering effect of the light from the electrolyte composition of the blood, blood flow rate, blood hematocrit level and other factors.
The optical density of blood corresponds to a number of factors and the measurement of the optical density of the blood has been used to determine certain blood parameters.
For example, during a hemodialysis session when fluid is being removed from the blood stream by a dialyzing machine, the concentration of hemoglobin, naturally occurring in the red blood cells, may decrease or, generally increase, with respect to the equilibrium processes of the fluid removal and mobilization from the body tissues. The change in the concentration of hemoglobin results in a corresponding change in the optical density of the blood and may be registered.
Monitoring changes in blood volume, as well as blood hemoglobin, can help to prevent such complications as hypotension due to continuous hypovolemia. Cardiac output of a patient, as well as other hemodynamic parameters of cardiovascular system, also provide useful information about the patient condition during hemodialysis, surgery, and in intensive care units. Using a dilution technique it is possible to calculate several characteristics of cardiovascular system, particularly cardiac output.
There are several research works and patents in the field of photometric blood monitoring. As shown in U.S. Pat. No. 3,830,569 to Meric; U.S. Pat. No. 4,243,883 to Schwartzmann; and U.S. Pat. No. 4,303,336 to Cullis, a device with suitable light source and photodetector may be used. Multiple detectors may be used, as shown by Meric.
As illustrated by U.S. Pat. No. 4,745,279 to Karkar et al.; U.S. Pat. No. 4,776,340 to Moran et al.; U.S. Pat. No. 5,048,524 to Bailey; and U.S. Pat. No. 5,066,859 to Karkar, additional detectors may be used to compensate various measurement artifacts, particularly for variations in intensity of light entering the blood stream.
However, the correlation between blood parameters and data obtained by photometric methods needs to be enhanced.
In U.S. Pat. No. 5,331,958 to Oppenheimer, a through photodetector and a remote photodetector are used for correction of light scattering due to sodium concentration fluctuations in the blood. Signals of the through and the remote photodetector are amplified separately. The data from the remote detector is used to compensate or adjust the data of the through detector. These and other dual correction or compensation systems are subject to the inherent unreliability of multiple detectors, as well as calibration issues.
A disadvantage of other methods of photometric analysis of blood properties, which utilize conventional external tubing, includes a dependence on the physical characteristics of the tubing such as diameter, wall thickness, and light absorption factor.
Therefore, the need exists for a method and apparatus which require only a single light detector, wherein the light scattering effect is eliminated or minimized. In such an apparatus, the mechanical construction and data collection process is substantially streamlined as compared to multiple photodetector devices. There is a need for a method and apparatus having automatic calibration of the optical probe sensitivity for each particular tubing that the probe is employed with; and further having a dilution technique applicable for determining hemodynamic parameters of a patient.
In accordance with the present invention, there is a novel method and apparatus for the photometric analysis of blood properties. The present design allows for registration of blood optical density, provides signal adjustment for fluctuations in light scattering, which are related to blood electrolyte composition, as well as blood flow rate and other blood parameters.
The present apparatus employs a single light emitter projecting a light beam along an illumination axis and a single receiving photodetector for measuring light along a detection axis, wherein the illumination axis is non colinear, offset or angled with respect to the detection axis. According to the method, the present invention includes projecting a light beam into a blood column along an illumination axis, and detecting the light emerging from the blood column by a single receiving photodetector receiving system along a detection axis that is non colinear to the illumination axis.
The effects of light scattering are taken into consideration and have been eliminated by the location and orientation of the single receiving photodetector detection axis with respect to the illumination axis. It is understood the present system may be employed with additional sensors or detectors, however these sensors are not required, or related to the light scattering compensation, but are employed for different purposes.
Preferably a light emitter of isobestic wavelength is used to avoid the effect of hemoglobin oxygen saturation.
The device may be used with an extracorporeal tubing system through which blood flows, as well as being applied to patient"" vessels and body tissues which are capable of being transilluminated. Further, the device may be used during a dialysis session as well as surgeries, intensive care procedures, measurements hemodynamic parameters of blood by dilution technique, or other blood property altering events.
The present method includes utilizing biologically natural indicators, as for example isotonic saline, glucose, or another solution, for measurements by dilution technique and calibration procedures. There is no need in special markers, such as dye-green or the like, which stay in a patient""s body for a long time.
In the drawings and in the detailed description of the invention there are shown and described only principal embodiments of this invention and are of illustrative nature only, but not restrictive. Other embodiments and technical realizations are applicable, all without departing from the scope and spirit of the invention.